Yu Gao, the China director for Landesa, a group working on land tenure issues, focused on the lack of what he called “social infrastructure” in China — mechanisms to protect the rights of those on the move in the country’s great urban migration.

Andrew Stokols, a writer and analyst of urbanization, discussed his recent travels in what he calls “China’s Wild West.”

Karen C. Seto, a professor of geography and urbanization at Yale University, warned against too much of a focus on China’s “eco cities” and megacities, given that the greatest migrations — and greatest prospect for change lay in a constellation of small cities far from the central government and media spotlight.

Here are the other sessions, which — before the day is out — will include my panel on transportation issues and opportunities in New York City and other metropolises and a fun conversation with the filmmaker Darren Aronofsky, who infused various environmental themes into his new epic feature film, “Noah“:

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By 2050 or so, the human population is expected to pass nine billion. Those billions will be seeking food, water and other resources on a planet where humans are already shaping climate and the web of life. Dot Earth was created by Andrew Revkin in October 2007 -- in part with support from a John Simon Guggenheim Fellowship -- to explore ways to balance human needs and the planet's limits.